Low-temperature, moderate-temperature and high-temperature heat pipes vary from each other in terms of the conventional cooling materials they are filled with. For example, low-temperature heat pipes are filled with water and applied to an ambient temperature below 100° C. Moderate-temperature heat pipes are for use at an ambient temperature of 200˜500° C. High-temperature heat pipes are for use at an ambient temperature above 500° C. Therefore, the cooling materials for filling high-temperature heat pipes are preferably alkali metals, such as metallic lithium, metallic sodium, and metallic potassium.
With alkali metals being of a low density, a low melting point and a low boiling point, alkali metals usually exhibit high activity capacity under a normal condition. If alkali metals are filled into a metallic pipe to manufacture a high-temperature heat pipe, the alkali metals will be likely to undergo chemical reactions upon exposure to air or water and therefore explode, thereby injuring filling workers.
Therefore, it is important to provide a filling pipe for use in high-temperature heat pipe filling operation to enable filling workers to fill solid alkali metals into a metallic pipe easily and safely in order to manufacture a high-temperature heat pipe.